Electron beam delection system



March 16, 1965 w. F. WESTENDORP ETAL 3,174,034

ELECTRON BEAM DEFLECTION SYSTEM Filed Dec. 28, 1962 //7 van/0m:

W/Y/em F Wes/endow,-

Sfep/ven Tamar,

5 by PDW United States Patent Ofifiee 3,174,084 Patented Mar. 16, 19653,174,084 ELECTRON BEAM DEFLECTION SYSTEM Willem F. Westendorp andStephen Tamor, Schenectady,

N.Y., assignors to General Electric Company, a corporation of New YorkFiled Dec. 23, 1962, Ser. No. 248,072 11 Claims. (Cl. 317-20i3) Thepresent invention relates to improved means for deflecting the electronbeam in electron beam apparatus such as a cathode ray tube.

Cathode ray apparatus is utilized for irradiating mate rials with a beamof high energy electrons. Usually the material to be irradiated isplaced on a moving belt that passes under the window of the cathode rayapparatus from which the electron beam emerges. A deflection system inthe cathode ray apparatus usually deflects the electron beam laterallyin a direction normal to the direction of movement of the belt so thatthe electron beam irradiates the total surface area of the material in aline by line manner.

Cathode ray apparatus usually is provided with a vac uum tight envelopeincluding a neck portion for enclosing the electron gun and acceleratingelectrode, and an extension thereof of triangular longitudinalcross-section which provides a drift region in which the electron beamis an-gularly deflected. The lineal width of material the beam can reachis limited by the size of the extension, and by the angular deflectionthe beam can achieve while still effectively reaching the material. Aconventional method of extending the deflection is to increase thelength of the drift region extension. However, cathode ray apparatus isalready undesirably long. For example, for a width of deflection of 38inches, cathode ray apparatus with a conventional deflection systemwould have a vacuum extension chamber approximately feet long.

Accordingly, an object of the present invent-ion is to provide cathoderay apparatus having a wide deflection but a short vacuum extensionchamber.

A further object is to provide a deflection system for an electron beamapparatus that produces a wide deflection of an electron beam in a shortdrift region.

It is a disadvantage of utilizing conventional approaches to extendingthe width of deflection of an electron beam that the angle at which thebeam strikes the irradiated material varies along the width of thematerial as the beam is angularly deflected. Consequently, theirradiation is not uniform along the width of material.

Hence, another object of the present invention is to provide cathode rayapparatus for irradiating material substantially uniformly across thewidth of the material.

A further object of the present invention is to provide a widedeflection of the beam in electron beam apparatus in which the angle ofincidence for the electron beam is substantially constant for all anglesof deflection.

These and other objects are achieved in one embodiment of our inventionby utilization in an electron beam deflection system of two magneticfields, one of which produces the lateral deflection scan of theelectron beam and the other directing the electron beam approximatelynormally to the target or the material irradiated, regardless of theangle of initial deflection of the electron beam.

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, together withfurther objects and advantages thereof all may best be understood byreference to the following description, taken in connection with theaccompanying drawings in which:

FIG. 1 is a cross-sectional side view, partially broken away, of avacuum chamber of cathode ray apparatus including an embodiment of adeflection system of our invention; and

PEG. 2 is a cross-sectional side view of FIG. 1.

Referring now to FIGS. 1 and 2, there is illustrated the portion 19 ofthe neck of the envelope of a cathode ray tube along which a beam ofelectrons 12 is formed and accelerated by any suitable means (not shown)such as an electron gun and accelerating electrodes. Since suitablemeans for generating and accelerating electron beams are well known, andthe particular means employed are not pertinent to the presentinvention, the means for gen. erating and accelerating electron beam 12have been omitted from the drawings for simplification.

Electron beam 12 passes into a vacuum extension chamber 14, and throughit along any one of an infinite number of paths A, B, C, D, etc., theparticular path depending upon magnetic deflection fields therein whichare to be subsequently described. Most of the electrons in beam 12 passthrough a thin window 16 of light material such as beryllium which isimpermeable to air so that the vacuum in chamber 14 is maintained. Afterpassing through window 16 beam 12 strikes material 13. Material 18 maybe moved in a direction normal to the present apparatus, e.g., out ofthe drawing, on a moving belt 20 so that as beam 12 is deflected backand forth across the width of chamber 14, it strikes the whole area ofthe surface of material 18 in a line-by-line manner.

As beam 12 leaves neck 1d and enters chamber 14- it is deflected by analternating current magnetic field from circular radially laminated polepieces 22 energized by a magnetic circuit and windings 24 coupled to anAC. current source 26. The deflection current from source 26 may be asine wave or a linear wave arranged to cause linear deflection of theelectron beam across material 18. The magnetic field across pole pieces22 is preferably constant for a given instantaneous value of current.The angle of deflection of the electron beam as the electron beam passesbetween the circular pole pieces is equal to an angle 6 where tan 2 isequal to where a=-radius of the pole pieces and R=r=adius of curvatureof the electron path in the magnetic field produced between the polepieces. Since for given electron energy, the radius R is inverselyproportional to the magnetic flux density B, and B is proportional tothe magnetizing current i, from the source 26, we may write tan =biwhere b is a constant.

According to the invention, it is now desired to redirect this angulardeflection of the electron beam so that electron beam for any angle 6meets window 16 substantially perpendicular to the window. It is also ingeneral quite (a desirable to have a simple relationship between lineardeflection, A, along the output window as measured, e.g., from thecentral axis of the system, and the current i which causes the firstdeflection at pole pieces 22. Then a given deflection current applied tocoils 24 will cause a controllable linear deflection A. In theembodiment of FIGS. 1 and 2, the linear deflection, A, is arranged to bedirectly proportional to the current i, whereby constant velocityelectron beam scanning corresponds to linear change of current withtime. In the principal embodiment of FIGS. 1 and 2, there is accordinglyprovided second pairs of deflection pole pieces 23-30 and 32-34. Theelectron beam passes between the members of one pair or the otherdepending upon the deflection already imparted to the beam by polepieces 22. Pole pieces 28- 30 or 32-34 act in the same manner as polepieces 22 and produce another angular deflection of the electron beam.However, the pole pieces 28-30 and 32-34 are shaped to cause angulardeflection of the electron beam substantially the reverse of thatoriginally imparted thereto by means of pole pieces 22. The newdeflection takes place along an arcuate path, desirably at a constantturning radius or radius of curvature, as the electron beam passesbetween a pair of pole pieces. The arcuate extent or width of the polepieces along the electron beam path is preferably just sufficient forredirecting the electron beam perpendicularly of the window, at aconstant beam turning radius, for any initial electron beam path between=90 and 0=-90.

In order for each path to have a constant radius, it is preferred tomagnetize the pole pieces 28-30 and 32-34 with a steady magnetic fieldprovided by means of a magnetic circuit 36 and magnetizing coils 38energized with direct current. This provides a radius of curvature, p,which is constant for the electron beam passing between a set of polepieces. For convenience the radius of curvature p is made equal to halfA where A, is the maximum lateral deflection at path G. A is the lineardeflection that corresponds to a maximum deflection current, i indeflection coils 24, and in which case 0:9 the maximum feasible initialangular deflection. In the embodiment shown the pole pieces 30 and 32are north poles in the magnetic circuit, and pole pieces 38 and 34 aresouth poles.

The pole piece pairs are situated such that, in addition to causing thechange in angular deflection of the electron beam in the reverse senseto that caused by pole pieces 22, the pole piece pairs also establishthe desired linear relation between the deflection current from source26 and the lateral deflection A at the output window. These relationscan be set up in the following manner: As previously stated,

0 a tan For convenience, the above ratio As previously mentioned, Atakes place at maximum deflection current in coil 24- and when 6:90".

In order to determine the extent of the pole piece pairs, radial linesmay first be drawn from the center of round pole pieces 22, for example,a line 40 in PEG. 1 at a given A=A tan 3 developed above. This value Ais marked by a vertical line, e.g., line 42 in FIG. 1, corresponding toelectron beam path F. The lines 4% and 42 are then joined with acircular electron beam arc of radius ,0, which, as above indicated, isconveniently chosen to equal half A The arcuate extent or Widthdimension of the pole pieces 30 and 34 for electron path P areestablished in this manner. The pole pieces extend along path P betweena point 44 where the arcuate deflection must start and a point 46 whereit should end in order for the beam to pass perpendicularly through thewindow. A similar construction may be made for other electron paths,i.e. paths A through G, to establish other points on the shape of thepole pieces. Pole pieces 28 and 32 are reflections of pole pieces 30 and34, or their dimensions may be graphically determined in a similarmanner.

It is seen the shape of the pole pieces is determined so the electronbeam leaves the area of the pole pieces at the desired angle and at adesired distance, A, from the center of the system, for any initialdeflection between and +90".

The shape of the pole piece pairs may also be calculated mathematically.It can be shown the bottom edge of each of the above described polepieces forms a curve having the following formula:

2A... 2 2 Here the ordinate, Z, is measured vertically down from ahorizontal line through the axis of the round pole pieces 22. Theequation represents a parabola with the vertical axis of symmetry at A:/2A and an apex at Z=%A The curve of the upper edge of the pole piecepairs can best be expressed around the center of round pole pieces 22 ata radial distance r, where tan 2 sin 0 Various departures from thepreferred embodiment are possible within the scope of the presentinvention. For example, although it is preferred the electron beams exitperpendicularly from window 16, it is appreciated the pole pieces can beoriented such that various electron beam paths all exit at some othercommon direction, or have some given spread relative to one another.Also, pole pieces 22 need not be round but can take other shapes, withpole pieces 28 to 34 acting to compensate such irregularities. Moreover,although it is usually convenient for the electron beam paths to exit inthe same direction but spaced from the axis of entering beam 12, theelectron beam 12 may enter at some other convenient angle. In such case,it is desirable to regard the electron beam paths exiting from window 16as achieving a deflection relative to a selected axis, i.e., the axis ofundeflected path A, rather than relative to the initial path of electronbeam 12.

It is also appreciated the electron beam deflection may be made thefunction of some other electrical input parameter, e.g. voltage ratherthan deflection current. Furthermore, a non-uniform flux density may beprovided along the pole piece pairs 28-30 and 32-34 with the shape ofthe pole pieces allowing for such non-uniformities as may occur withtime or with deflection along the pole pieces.

Wide beam deflection is accomplished in accordance with the presentinvention and is produced within a comparatively short beam path lengthallowing the overall tube to be relatively short.

While we have shown and described several embodiments of our invention,it will be apparent tothose '5 skilled in the art that many otherchanges and modifications may be made without departing from ourinvention in its broader aspects; and we therefore intend the appendedclaims to cover all such changes and modifications as fall within thetrue spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUni-ted States is:

1. A system for producing Wide deflection of an electron beam from aninitial path relative to a selected axis comprising first means forperiodically scanning said electron beam at an angle to said selectedaxis and magnetic deflection means for producing an arcuate directionchange in said electron beam to a direction substantially parallel tosaid selected axis.

2. A system for producing wide deflection of an electron beam from aninitial path relative to a selected axis comprising first means forperiodically scanning said electron beam at angles to said selected axisin response to an electrical parameter and magnetic deflection means forproducing an arcuate direction change in said electron beam to a secondpath substantially parallel to said selected axis, wherein theseparation between said second path and said selected aXis isproportional to the said electrical parameter.

3. A system for producing wide deflection of an electron beam from aninitial path comprising first magnetic means for periodically scanningsaid electron beam through a first changing angle in a first deflectiondirection and second magnetic means for deflecting said electron beamthrough the same angle in the reverse deflection direction to cause saidbeam to follow a second path substantially parallel to said initialpath.

4. A system for producing wide deflection of an electron beam from aninitial path comprising first magnetic means for continuously scanningsaid electron beam at a varying angle to said initial path in responseto a continuously varying deflection current, a function of said anglebeing proportional to said deflection current, and second magnetic meansfor producing an arcuate direction change in said electron beam to asecond path substantially parallel to said initial path, wherein theseparation between said paths is also proportional to said function ofsaid angle and therefore proportional to said current.

5. A system for producing deflection of an electron beam from an initialpath comprising first means for deflecting said electron beam tocontinuously varying angles relative to a selected axis in response tovarying deflection current, and magnetic means having magnetic polepieces generating a constant D.C. field for producing an arcuatedirection change of constant radius but varying arc length in eachelectron beam path to a final direction substantially parallel to saidselected axis, said magnetic pole pieces having a face width adjacentthe electron beam path proportioned to produce said arc length at aconstant turning radius.

6. A system for producing deflection of an electron beam from an initialpath comprising first means for scan ning said electron beam at acontinuously varying angle relative to a selected axis in response to achanging deflection parameter, and magnetic means having magnetic polepieces generating a constant D.C. field for producing an arcuatedirection change of constant radius but varying arc length in thevarying electron beam path to a final direction path substantiallyparallel to said selected axis, said magnetic pole pieces having a facewidth adjacent said electron beam path proportioned to produce said arclength, and said pole pieces being positioned to provide a deflectiondistance between initial and final electron beam paths proportional tosaid parameter.

7. A system for producing wide deflection of an elec tron beam from aninitial path and relative to a selected axis comprising first means fordeflecting said beam to a second path of varying angle in response to achanging deflection parameter, and second means for producing adirection change in said second path to a final path in a directionsubstantially parallel with said selected axis at a distance therefromproportioned to said deflection parameter, each said arcuate directionchange having an arc length and radius of curvature smoothly joiningsaid second and said final paths.

8. A system for producing a wide deflection of an electron beam from aninitial path comprising first means for directing said electron beam toa varying second path in response to a changing deflection parameter,and second magnetic deflection means for producing an arcuate directionchange in said second path to a third path parallel to said selectedaxis, said arcuate direction change having an arc length and a commonradius of curvature for smoothly joining said second and third paths.

9. A system for producing wide deflection of an electron beam from aninitial path comprising first circular magnetic pole pieces disposed oneither side of said electron beams initial path, a coil and a magneticcircuit for energizing said magnetic pole pieces in response todeflection; a varying current causing a magnetic field between said polepieces varying with time and producing a first varying angulardeflection of said electron beam as a function of said deflectioncurrent, second magnetic pole pieces disposed on either side of saidelectron beam as deflected for producing a steady magnetic field causingdeflection of said electron beam in a reverse sense at a relativelyconstant radius of curvature between said second pole pieces, saidsecond magnetic pole pieces being extended along electron beam paths tocause a change in direction thereof to a direction parallel to saidselected axis at a distance therefrom in proportion to said deflectioncurrent.

10. A system for producing wide deflection of an electron beam from aninitial path comprising first circular magnetic pole pieces disposed oneither side of said electron beams initial path, a coil and magneticcircuit for energizing said magnetic pole pieces in response to anoscillatory deflection current causing a scanning magnetic field betweensaid pole pieces and producing a first changing angular deflection ofsaid electron beam as a function of said deflection current atdeflection angles between zero for zero deflection current and formaximum deflection current, second magnetic pole pieces disposed oneither side of said electron beam as initially eflected for producing asteady D.C. magnetic field causing a deflection of said electron beam ina reverse sense to its first deflection at a relatively constant radiusof curvature, the extent of said second pole pieces relative to saidelectron beam at a first deflection of 90 establishing a maximum lineardeflection of said electron beam to a path substantially parallel tosaid first path, and wherein said second pole pieces relative to saidelectron beam path have an extent along the beam for producingdeflection of said electron beam to a final path parallel to said firstpath, the distance between said final path and said first path asdivided by said maximum linear deflection equaling the ratio between thedeflection current corresponding to said final path and the maximumdeflection current.

11. A system for producing wide deflection of an electron beam from aninitial path comprising first circular magnetic pole pieces disposed oneither side of said electron beams initial path, a coil and magneticcircuit for energizing said magnetic pole pieces in response toalternating deflection current causing a substantially uniform magneticfield between said pole pieces at a given point in time and producing afirst varying angular deflection of said electron beam as a function ofsaid deflection current, where the tangent of half the angle ofdeflection equals bi, where i is the current in said deflection coil andb is a constant, said tangent also equaling aweoaa Where a is the radiusof the circular pole pieces and R is the radius of curvature of theelectron path in the field of the pole pieces, second magnetic polepieces dispose on either side of said electron beam as first deflectedfor initial deflection angles between -90 and +90", said second magneticpole pieces producing a steady DC. magnetic field for causing deflectionof said electron beam in a reverse sense to the first deflection and ata relatively constant radius of curvature between said second polepieces, the extent of said second pole pieces relative to said electronbeam at a first deflection of 90 establishing a maximum lineardeflection of said electron beam, A to a path perpendicular to saidfirst path, wherein the said second pole pieces relative to saidelectron beam path have an extent for producing deflection first pathwherein of said electron beam A to a final path parallel to said UNITEDSTATES PATENTS 2,897,365 7/59 Dewey et al 313-76 2,909,688 19/59 Archald317-200 2,941,077 6/60 Marker 317-200 3,013,154 12/61 Trump 317-200LARAMIE E. ASKTN, Primary Examiner.

FGHN F. BURNS, Examiner.

1. A SYSTEM FOR PRODUCING WIDE DEFLECTION OF AN ELECTRON BEAM FROM ANINITIAL PATH RELATIVE TO A SELECTED AXIS COMPRISING FIRST MEANS FORPERIODICALLY SCANNING SAID ELECTRON BEAM AT AN ANGLE TO SAID SELECTEDAXIS AND MAGNETIC DEFLECTION MEANS FOR PRODUCING AN ARCUATE DIRECTIONCHANGE IN SAID SLECTRON BEAM TO A DIRECTION SUBSTANTIALLY PARALLEL TOSAID SELECTED AXIS.